Although the Fexl language itself has syntax for recursive definitions, it translates everything to combinators internally, so there are no "symbol tables" or "environments" at run time. Therefore it uses the Y combinator to implement those recursive definitions.
I would say that the y-combinator is interesting to the such a degree that it becomes useful. Sure you won't and shouldn't use the y-combinator in any real world applications. But first off it demonstrates the true power of the lambda calculus to represent computation, and more importantly to the practical programmer is that understanding it will provide a deep insight into the nature of computation, which is profoundly useful if you ask me.
It's a stretch to say that you shouldn't use them in a real application. Combinators in general can be useful for implementing functional programming languages, and those languages can be useful for applications.
That may sound like bickering over a fine point, but I'm just saying that combinators can be more than a theoretical tool.
It's useful for lambda functions that recursively call themselves, you don't need these in practice because you wouldn't use a lambda. You would use a named function, therefore, they are almost purely theoretical aspect of Lambda Calculus. I can't think of any programming language that is purely lambda calculus.
I've never understood why y-combinator is useful or impressive. Interesting, maybe, but not really useful.